Field of the Disclosure
The present disclosure relates to a tool changer that changes a tool attached to a spindle of a machine tool with a next tool positioned at a standby position.
Background of the Disclosure
Various types of tool changer have been known; among them, a so-called double arm type tool changer is generally used at the present time. This type of tool changer is configured to include a holding member disposed to have a center axis parallel to an axis of the spindle and provided to be rotatable about the center axis and to be movable in a direction along the axis of the spindle, a rotating mechanism for rotating the holding member in normal and reverse directions about the center axis, a forward/backward moving mechanism for moving the holding member forward and backward in the direction along the axis of the spindle, a tool change arm (double arm) having two arm portions each disposed on the holding member to extend in a radial direction with respect to the center axis of the holding member so that they form a straight line and each having a tool holding part that has an opening in a side surface thereof facing the normal rotation direction of the holding member, the arm portions holding the tools with the tool holding parts in such a manner that axes of the tools are parallel to the center axis of the holding member, and a controller controlling the rotating mechanism and the forward/backward moving mechanism.
Further, well-known examples of the tool changer having the above-described configuration include a hydraulic type using hydraulic pressure as a drive source for the rotating mechanism and the forward/backward moving mechanism, a type using a cam mechanism driven by an AC motor (cam driving type), a type using a servo motor (servo motor driving type) as disclosed in Japanese Unexamined Patent Application Publication No. 2000-193062 and Japanese Examined Utility Model Application Publication No. H8-4990. The hydraulic type tool changer was used at the early stage of development, and the cam driving type tool changer was developed thereafter for the purpose of shortening changing time. Further, in recent years, the servo motor driving type tool changer has been employed because advances in technology for the driving mechanism, such as increase in servo motor speed, has enabled the tools to be changed in less time than using the cam driving type tool changer.
By the way, in the servo motor driving type tool changer, a servo motor as a part of the rotating mechanism (rotation driving servo motor) and a servo motor as a part of the forward/backward moving mechanism (forward/backward movement driving servo motor) are controlled by the controller. Further, the servo motor driving type tool changer is configured so that an angular position of the tool change arm is detected by an encoder attached to the rotation driving servo motor (rotation encoder) and similarly a forward/backward movement position of the tool change arm is detected by an encoder attached to the forward/backward movement driving servo motor (forward/backward movement encoder).
More specifically, an angular position of the tool change arm is calculated from current number of revolutions and angle of rotation (rotational position data) of the rotation servo motor, which are detected as absolute values (which means that they are not relative values; the same is applied hereinafter) by the rotation encoder, and a reduction ratio of a transmission mechanism, which transmits power of the rotation servo motor to the holding member to rotate the holding member, relative to the rotation servo motor.
Further, a forward/backward movement position of the tool change arm is calculated from current number of revolutions and angle of rotation (rotational position data) of the forward/backward movement servo motor, which are detected as absolute values by the forward/backward movement encoder, and a lead of a ball screw mechanism that transmits power of the forward/backward movement servo motor to the holding member to move the holding member forward or backward.
Further, the tool change arm is controlled by the controller; the rotation thereof is controlled based on the rotational position data of the rotation servo motor detected as described above and a rotation zero point that is set as appropriate from the rotational position data, and the forward/backward movement thereof is controlled based on the rotational position data of the forward/backward movement servo motor and a forward/backward movement zero point that is set as appropriate from the rotational position data.
Noted that the rotation encoder has a memory therein and data detected by the rotation encoder is held as rotational position data in the memory. Similarly, the forward/backward movement encoder also has a memory therein and data detected by the forward/backward movement encoder is held as rotational position data in the memory. Further, the holding of the data in each memory is realized by electrical power supplied from the controller or a back-up battery through an appropriate cable. Furthermore, data on the rotation zero point and data on the forward/backward movement zero point are stored in the controller.